metal boat and welding inspection

Discussion in 'Metal Boat Building' started by lance linked, Sep 30, 2015.

  1. lance linked
    Joined: Sep 2015
    Posts: 25
    Likes: 1, Points: 0, Legacy Rep: 34
    Location: Pennsylvania, USA

    lance linked Junior Member

    In another thread that got locked for derailure, the question was asked, "How can you tell the strength of a weld by NDT?" The respondents concluded that it is not possible to do so. This is not true.

    As a welding engineer/inspector specializing in steel products I am asked the question from time to time, and answer that there is a direct correlation between BHN (hardness) and tensile strength. This correlation is material specific, and is best empirically determined, as formulae only work within given range values. Here is a link to a good chart that works with mild HSLA steels typical of boat building steels, as well as steels in the upper strength ranges:

    So, to calculate UTS you need to know BHN? You can determine BHN on any given weld en situ with a grinder and a portable tester known as a Tele-Brinnel device:

    A Tele-Brinnel device uses a hammer to produce a divot on any flat polished steel surface that can be compared in diameter using an optical micrometer with a proof divot produced in the same action on a reference bar of known hardness. The results of the comparison are interpreted with a standardized reference chart, yielding BHN actuals. T-B is best between 35 and 400 BHN. Higher hardness steels (of no interest to us) are tested with Vickers or Rockwell method by electronic device.

    Also mentioned in that thread is destructive testing of a mock-up sacrificial blank, welded in strict conformance with planned and stated welding parameters, which can be regarded as representative of production welding with similar strict parameter/procedure control. This is standard practice with all types of welding, usually required by code and contract.

    The question of how a weld quality/porosity can be assured was also broached. Visual, Penetrant, Mag Particle, and X-ray testing were mentioned, and are variably effective, depending to a degree on what final condition of weld (as-welded, grind smooth, etc). As a certified inspector, I am familiar with these practices and can attest to their value.

    I am a steel products manufacturing and quality engineer/inspector with 25 years experience in the industry, and would be glad to help in the future with any other steel or welding related questions.
    1 person likes this.
  2. Oleboynow

    Oleboynow Previous Member

    building under Lyoyds I used the bend tests set out in the British Standards
    On site x rays in the early years
    Being alu, we leave the weldment for test au naturale, because grinding just introduces grit into the metal
    In starting a new employee I always got him or her to sample weld plates, which included the prep of edges, a nick break test and the mandrel roll test
    It takes 5 years to produce a welder who can constantly produce class welds in any position
    The problem these days is that people do not understand the machine
    Machines are programmed, In my day we had to understand the corrolation between amp, volts and wire speed
    As for SMAW, it seems a forgotten art
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.